Expert: Sherry Wallin - 9/23/2009

Question
I need to write a rule for this. input, x 10,11,12,13 and output, y 3,4,5,6,. I'm not sure how to do this.

Answer
What is the change in y? What is the change in x? What is the slope of a line? The change in y over the change in x, so find the slope and then use y-y1=m(x-x1) to write the equation of the function in point slope form and then solve for y to put in slope intercept form.



It appears that I didn't give you enough help so please just ask for more specifics.

You have 4 values of x and 4 values of y and each is associated with the other so you have 4 ordered pairs: (10,3), (11,4), (12,5), (13,6). Use any two to calculate the slope: I will use the first two:
(4-3)/(11-10) = 1/1. So y changes by 1 as x changes by 1 so m = 1/1. Now you have the slope m and you can use any of the 4 points to write thae equation using the point slope formula: y-y1 = m(x-x1) ->
y-3=1(x-10) -> y-3 = x - 10 -> y = x-7 nd there is your 'rule', better??

Math Prof